Sonotube Concrete Calculator
Calculate concrete needed for round Sonotube column footings from tube diameter, depth, and count.
Shows cubic yards plus 60 and 80 pound bag counts.
Sonotube is the common brand name for the cardboard tube forms used to pour round concrete columns and footings, the kind that hold up decks, fences, mailboxes, and porch posts. Working out the concrete needed is just the volume of a cylinder, repeated for however many tubes you are pouring.
The volume of one tube is pi times the radius squared times the height. The trick is keeping units consistent: the diameter is given in inches but the depth is usually in feet, so convert the radius to feet before multiplying. For example, a 10-inch tube has a radius of 5 inches, or about 0.417 feet, so a 4-foot-deep footing holds roughly 2.2 cubic feet. Multiply by the number of tubes and divide by 27 to get cubic yards.
From there you can decide how to buy the concrete. An 80-pound bag of mix yields about 0.6 cubic feet and a 60-pound bag about 0.45, so a single deep footing can swallow several bags fast. Once the total passes roughly one cubic yard, a ready-mix truck is usually cheaper and far less work than mixing dozens of bags by hand.
Always pour a little extra. A flared or belled base, or a footing pad under the tube, adds volume the plain cylinder math misses, and a column that runs short near the top leaves a weak cold joint. Round up rather than down, and brace the tubes well so they do not float or shift when the wet concrete goes in.